A mumps epidemic has broken out in the Netherlands, which was the first time in 20 years, Dutch media reported Monday.

The epidemic concentrated in the stretch of land between Zeeland in the southwest and the Veluwe heathlands in central Netherlands, the so-called "Bible belt" where many orthodox Protestants live.

Many people in the area refuse to have their children vaccinated against mumps and other diseases on religious grounds.

Mumps have been diagnosed in more than 60 blood samples over the past few months but the public health institute (RIVM) said the real number could be much higher because doctors are not legally obliged to report cases to the authorities.

The "Bible belt" was also hit by polio and measles epidemics in the 1990s.